(a) Field of the Invention:
The present invention relates to an incandescent lamp unit for use as an automotive headlight, and more particularly to an incandescent lamp unit of which a glass bulb has formed at the rear end thereof a pinched portion of a rectangular section having two opposite wide side faces and two opposite narrow side faces and which is held by a supporting plate or base made of a resilient metal.
(b) Related Art Statement:
The incandescent lamp units of this type are well known. One of them is disclosed in the Japanese Examined Patent Publication No. 58-12706. FIGS. 1 to 3 show such a conventional incandescent lamp unit of which a bulb 1 has formed at the rear end thereof a single pinched portion 2 which is rectangular in sectional form. As shown in FIG. 2, the pinched portion 2 has wide side faces 21 and narrow side faces 22. A filament 23 is disposed in the sealed inner space of the bulb 1, and lead-in wires 15 connected to the filament 23 are laid as buried in the pinched portion 2, led out at the lower end thereof and connected to terminals 16. The reference numeral 3 indicates a single disk-shaped, bulb-supporting plate or base made of a resilient material. The base 3 has various cuts therein by punching. The cuts inlcude a one extending longitudinally in the center of the base 3 and two small oblique cuts each adjoining the longitudinal cut. Thus, two lugs 6 are formed of which the ends are resiliently engaged each in a recess 17 formed in each of the wide side faces 21 of the pinched portion 2. Also a triangular lug 8 is formed by the oblique cutting at each end of the longitudinal cut in the base 3 and abuts each narrow side face 22 of the pinched portion 2. These lugs 8 are bent down from the base 3 perpendicularly to the axis of the longitudinal cut and thus defines the narrow sides of the elongated opening 7 (longitudinal cut). The pinched portion 2 of the bulb 1 is inserted into the opening 7 in the base 3 and the lugs 6 are elastically engaged on the wide side faces 21, respectively, of the pinched portion 2 while the lugs 8 are engaged on the narrow side faces 22 so that the pinched portion 2 is held in the base 3. The base 3 is fixed to a cylindrical holder 18 by calking or otherwise.
In the conventional incandescent lamp unit, the lugs 6 and 8 which are engaged on the pinched portion 2 to hold the latter are made by working the bulb-supporting plate or base 3 by punching; therefore, the lugs 6 engaged on the wide side faces 21 have the width L thereof limited to approximately a half of the width D of the elongated opening 7 as shown in FIG. 3. The width D is made nearly equal to, or somehow larger than, the distance between the wide side faces, namely, the width of the pinched portion 2. Accordingly, the arm length of the lugs 6, that is, the width L, is substantially limited to about a half of the pinched-portion width, and so the ratio of the arm length of the lugs 6 to the length of the pinched portion 2, namely, the length of the pinched portion 2 along the led-out direction of the lead wide 15, is small. The larger this ratio, the more stably the bulb 1 is held by the base 3, but in the conventional lamp unit in which the lugs 6 are formed by punching the single base 3, there is a problem that the arm length of the lugs 6 cannot be made larger for the aforementioned reason.